Other copolymerizations

The kinetics of many copolymerizations have now been examined with absolute (overall) propagation rate constants being determined by the rotating sector, PLP or FSR methods. A similar situation as pertains for the MMA-S 

The values of sA and. ru are not well defined by kinetic data.59 61 The wide variation in. vA and for MMA-S copolymerization shown in Table 7.5 reflects the large uncertainties associated with these values, rather than differences in the rate data for the various experiments. Partly in response to this, various simplifications to the implicit penultimate model have been used (e.g. rA3rBA= W- and -Va=- h)- These problems also prevent trends in the values with monomer structure from being established. 

It has been pointed out that analysis of terpolymerization data or copolymerization with chain transfer could, in principle, provide a test of the model. 5 However, to date experimental uncertainty has prevented this. 

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Copolymerizations of benzvalene with norhornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorhornene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymeriza tion of acetylene with other monomers (33—39), and various techniques for grafting polyacetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubiUty increases. 

Copolymerization. The reactivity ratios of 1-hexene (M ) with 5-methyl-l,4-hexadiene (M2) were determined by copolymerization at 30°C in hexane solvent using a Et2AlCl2/6-TiCl3 AA catalyst system (Al/Ti atomic ratio = 1.5). Copolymerizations were conducted in 4-oz. bottles using concentrations of 10 g. monomer in 40 g. hexane and 5.0 mmoles TiCl3 per 100 g. monomer. All other copolymerizations were conducted under similar conditions. The reactivity ratios were calculated by the. Tidwell-Mortimer (22) computer method. The compositions of the copolymers were measured by using 300 MHz H-NMR. 

There is a tendency toward alternation in the copolymerization of ethylene with carbon monoxide. Copolymerizations of carbon monoxide with tetrafluoroethylene, vinyl acetate, vinyl chloride, and acrylonitrile have been reported but with few details [Starkweather, 1987]. The reactions of alkenes with oxygen and quinones are not well defined in terms of the stoichiometry of the products. These reactions are better classified as retardation or inhibition reactions because of the very slow copolymerization rates (Sec. 3-7a). Other copolymerizations include the reaction of alkene monomers with sulfur and nitroso compounds [Green et al., 1967 Miyata and Sawada, 1988]. 

The versatility of polymerization resides not only in the different types of reactants which can be polymerized but also in the variations allowed by copolymerization and stereoselective polymerization. Chain copolymerization is the most important kind of copolymerization and is considered separately in Chap. 6. Other copolymerizations are discussed in the appropriate chapters. Chapter 8 describes the stereochemistry of polymerization with emphasis on the synthesis of polymers with stereoregular structures by the appropriate choice of initiators and polymerization conditions. In the last chapter, there is a discussion of the reactions of polymers that are useful for modifying or synthesizing new polymer structures and the use of polymeric reagents, substrates, and catalysts. The literature has been covered through early 2003. 

Copolymerization is a facile method to diversify the structure of polymer materials. However, if the polymerizabiHties of comonomers are far from each other, copolymerization is essentially difficult, resulting in the formation of a mixture of the homopolymers and/or the copolymer with block sequences. This is the case for the anionic copolymerization of epoxide and episulfide, where the po-lymerizabihty of episulfide is much higher than that of epoxide, and the copolymer consisting mostly of -S-C-C-S- and -O-C-C-O- homo sequences is formed [87]. As mentioned in the previous sections, the zinc complex of /-methylpor-phyrin brings about polymerization of both epoxide and episulfide. 

RIS theory is used to calculate mean-square unperturbed dimensions 0 and dipole moments

of ethylene-vinyl chloride copolymers as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the vinyl chloride sequences. As was previously found for several other copolymeric chains, is much more sensitive to chemical composition and chemical sequence distribution than is 0. The present calculations also indicate that both and are most strongly dependent on chemicel sequence distribution for ethylene-vinyl chloride chains having vinyl chloride sequences which are significantly syndiotactlc in structure. 

Some systems actually behave as the Q - e scheme predicts while other copolymerizations deviate from the proposed pattern. On the whole, the scheme is regarded with some misgivings at present. It is quite clear that a complicated chemical reaction, comprising the mutual interaction of many kinds of radicals and molecules in various media, can hardly be described in its entirety... 

Calculations of copolymer composition are based on kinetic considerations and procedures. In spite of this, less attention has been paid to the copropagation rate than to other copolymerization problems. Today a single concise theory is available, solving the rate of the simplest radical binary copolymerization. Other cases described have not been generalized so far they treat the kinetic behaviour of specific monomer pairs or triplets in specific polymerization circumstances. 

Typically, copolymer composition can be manually adjusted by slowly feeding the more reactive monomer in throughout the reaction but this may not be helpful when trying to overcome monomer transport limitations. Therefore, Reimers and Schork [ 102] performed identical copolymerization experiments in miniemulsions, where monomer transport is less significant, in order to determine what effect this would have on the evolution of the copolymer composition. Data on the MMA/VS (and other) copolymerizations indicate that the Schuller equation (and not the Samer adaptation) fits the copolymer composition data. This points to the effect of extremely low monomer water solubility on copolymer composition in macroemulsion polymerization, and the relative insensitivity of miniemulsion polymerization to this effect. 

LCB-PE (long chain branched polyethylene) is not accessible through simple ethyl-ene/a-olefin copolymerization. Therefore, a bifunctional bimetallic catalyst was developed, in which one active center oligomerizes ethene to long-chain a-olefins, while the other copolymerizes them with ethene. 

If reactivity ratios are particularly disparate then it is possible to form a block copolymer from a batch polymerization. Thus the copolymerization of MAH with S by NMP or RAFT with excess S provides P(MAH-o/f-S)-i(> ocA -PS. There is a similar outcome in other copolymerizations which show a strong alternating tendency such as S with maleimides e.g. or AN. The... 

The fractions of homo- and heterodiads may be calculated from the reactivity ratios and feed composition assuming a simple copolymer (39) or other copolymerization model (40). It is still necessary to estimate Mark-Houwink constants for the hetero segments. A method has been suggested for this (37), but the entire procedure is quite tedious and is unlikely to be applied unless there is a need for many analyses of a particular copolymer. 

Basis Model. For many years, people believed that the terminal model was the basis of copolymerization propagation kinetics because it could be fitted to the composition data for most systems tested. However, in 1985 Fukuda and coworkers (7) demonstrated that the terminal model failed to predict the propagation rate coefficients for the copolymerization of styrene with methyl methacrylate— a system for which the composition data had been widely fitted by the terminal model (see Fig. 1). These results were later confirmed by several independent groups, both for the styrene-methyl methacrylate system (imder a wide range of different conditions), and also several other copolymerizations—indeed for almost all systems so far tested (37). It now appears likely that the failure of the terminal model to describe simultaneously the composition and propagation rate coefficients of ordinary free-radical copoljrmerization systems is general, with the terminal model being applicable only to those exceptional systems in which the comonomers have very similar reactivities. 

The fact that the neutral saccharide residue is trapped on the column and subsequently can be eluted as though it contains carboxylate functionality frirther supports the thesis that the saccharide monomer is incorporated into the poly(acrylic acid). In a control experiment, glucose was not retained on the ion exchange column in the presence of the copolymer while the copolymer was. These observations were used to advantage in the determination of saccharide monomer incorporation into the acrylic acid copolymer. A solution of polymer made from a feed containing 2 mole% monomer 5f that was not otherwise purified was subjected to the solid phase extraction technique. Forty-six percent of the saccharide present in the copolymer solution prior to solid phase extraction was not retained on the solid phase extraction medium 54% of the saccharide was retained and therefore bound to the copolymer. This indicates that a feed of 2 mole% of this saccharide monomer leads to the incorporation of 1.1 mole% monomer in the copolymer. Similar levels of monomer incorporation were observed in other copolymerizations of monomer 5f and with monomer 5e (75). 

Other monomers that copolymerize with alkyl vinyl ethers are vinyl ketones [47], acrolein diacetate [48], acrylamide [49], alkoxy 1,3-butadienes [50], butadiene [51], chloroprene [52], chlorotrifluoroethylene [53], tri-and tetrafluoroethylene [54], cyclopentadiene [55], dimethylaminoethyl acrylate [56], fluoroacrylates [57], fluoroacrylamides [58], A-vinyl car-bazole [59,60], triallyl cyanurate [59,60], vinyl chloroacetate [61,62], N-vinyl lactams [63], A-vinyl succinimide [63], vinylidene cyanide [64, 65], and others. Copolymerization is especially suitable for monomers having electron-withdrawing groups. Solution, emulsion, and suspension techniques can be used. However, in aqueous systems the pH should be buffered at about pH 8 or above to prevent hydrolysis of the vinyl ether to acetaldehyde. Charge-transfer complexes have been suggested to form between vinyl ethers and maleic anhydride, and these participate in the copolymerization [66]. Examples of the free-radical polymerization of selected vinyl ethers are shown in Table IV. 

In the next step, ethylene was copolymerized with 3-butenyl-Si(CH3)3 and the results were compared with those of the other copolymerizations [23]. With Et (Ind)2ZrCl2/MAO as catalyst, the 3-butenyl-Si(CH3)3 behaved like 1-alkenes if... 

The molecular weights of the copolymer prepared in the presence of naphthalene, in both the benzene and THF solvents, were lower than the corresponding copolymer prepared without naphthalene. The decline is attributed to chain-transfer reactions.From other copolymerization studies, in the absence of additives, it has been concluded the activation energy was 12.8 kcal/mol. 

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